The fresh cutted wood and the one with a humidity superior to 30%, stains with blue color, color that predominates generally, but also can acquire stains of other colors, like yellow, red, green and white. This phenomenon is more pronounced in a humid climate and not in a very cold one. The stains appear specially due to the growth of the fungi: 1) Ceratocystis species, like pilifera C., C. piceae (blue stain), 2) Ophiostoma species (blue stain), 3) Antirhynium sp. (blue stain), 4) Aureobasidium species (yellow stain) and 5) Fusarium sp. species (red stain).
The formation of stains in the sawed wood is a serious problem for the distant sawmills, where the tables and planks have to be piled up until being transported to the commercial centers where they will be used, because these stains can already appear in few days. Also, during the transport of humid wood in the store-rooms of ships, a fast appearance of the stains is caused by the fungi. This means a serious economic problem for Chile, which is a great exporter of wood to distant countries like United States, Europe, Arabia and Far East.
The exposed facts and the International Norms have motivated the search of solutions for the elimination of the phenomenon of the stains in the wood, which appearance means an obviously diminution of the price of the affected lignocellulosic products. There have been intents to fight the formation of stains by submerging the wood in liquids or by sprinkling liquids with different inhibitors of the growth of the fungi.
One of first compound which obtained good results was chloroorganic Pentachlorophenol. Nevertheless, already in the early 90s, its use was prohibited for its great toxicity (mutagenic, cancerogenic, liver damages). In general the chloroorganic compounds had great importance for their properties like fungicides, insecticides, plaguicides in general and chemical arms, but actually many of them had to be withdrawn of the market. Further the mentioned chloroorganics release the chlorodioxines to the environment, which enormous toxicity restricts even more the use of these chloroderivatives.
After that Pentachlorophenol was replaced by Tribromophenol, which obtained good results in the combat against the stains of the wood, but subsequently it was possible to verify that the bromocompounds also have a high toxicity. For that reason Tribromophenol has been replaced recently by compounds like Copper oxiquinolinate, PQ-8, also toxic, although also nonvolatile, actually very used. Oxiquinolinate is used together with Carbendiazime to reinforce its action. Metiolenbis-tiocianate/2-(T-Benzothiazol) is also used. All these substancies produce health problems (see table 1).
Among the disadvantages of Copper oxiquinolinate, PQ-8, can be mentioned in addition, that it has a relatively high price and that it dyes the wood yellow.
During the development of a process of accelerated petrifaction of wood and in general of lignocellulosic materials, patent request number 1332-2001, patent request number 2746-2002 and US publication number 2004/0105938 A1, (Jun. 3, 2004), could be observed that the liquid used for the treatment not only prevented the combustion of the wood, its putrefying and the attack of the termites, but also prevented the formation of stains by fungi. Afterwards studies were made to avoid the formation of stains by the treatment of the wood and in general of lignocellulosic material with liquids of a similar composition, including substances which nature allowed to suppose an utility. The realized tests allowed to choose a mixture of large shredss and alkaline benzoates in an middle alkaline medium as the most powerful inhibitors of the staining fungi. These ions also can be used besides the ions which are ingredients of the petrifaction of the wood, borates and silicates.
TABLE 1Toxicity of comercial antistain substancesCopper 8Carbendiazime/2,4,6oxiquinolinateCopper 8Metiolenbistiocianate/Tribromophenol(PQ-8)oxiquinolinate2-(T(Benzothiazol))LD50 acute>5.000 mg/kg3.900-4.700 mg/kg861 mg/kg280 mg/kgoral rat:LD50 acute>8.000 mg/kg>2.000 mg/kg2.020 mg/kg1.670 mg/kgtermal rabbit:Irritating orEyes, mucous andEyes and skinEyes and skinEyes and skincorrosive to:respiratory systemFormation ofYESNONONOdioxines: